Study: Extreme hurricanes hitting US more frequently

LOS ANGELES -- The question of whether or not global warming influences the strength or frequency of hurricanes is a matter of heated scientific debate.

Though some climate scientists argue that increased sea surface temperature and cyclone activity are linked, others say the evidence is ambiguous at best. Some contend that news media distortions and a lack of historical, standardized hurricane data only make it seem like the storms are worse.

Now, a new study is likely to stoke the debate even further. On Monday, a paper published in the journal Proceedings of the National Academy of the Sciences, or PNAS, concluded that large Katrina-sized hurricanes were twice as likely to form off the United States' southeast coast in hotter years than they were in colder years.

The analysis, which focused only on the North Atlantic, also concluded that the frequency of hurricanes with large storm surges has been increasing since 1923.

The study is unique in that it relies primarily on storm surge data taken from tide gauges along the Gulf Coast and Eastern Seaboard of the United States.

Other studies have relied on satellite imagery that has only been used for the last 40 years. The tide gauge data date to the 1920s.

Climate scientist and lead author Aslak Grinsted said that storm surges recorded by the tide stations were a good indication of tropical storms and of damaging hurricanes that made landfall.

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"We simply counted how many extreme cyclones with storm surges there were in warm years compared to cold years, and we could see that there was a tendency for more cyclones in warmer years," said Grinsted, of the Niels Bohr Institute of the University of Copenhagen.

Grindsted and his colleagues noted that hurricanes with the highest storm surges tended to cause the most damage. Storms the size of Hurricane Katrina, which hit New Orleans in 2005, make landfall every 10 to 30 years on average.

Gindsted posited that such storms would occur with greater frequency as global temperatures increased in the coming years, as models have predicted.